1. Field of the Invention
The present invention relates to a rack and pinion type oscillating actuator which converts a linear reciprocating motion into an oscillating motion via a rack and pinion.
2. Description of the Conventional Art
As shown in FIGS. 19 and 20, there has been known a rack and pinion type oscillating actuator 51 structured such that a pair of mutually parallel sliding holes 53 are formed in a body 52. Rack members 54 having racks 55 formed in parts of the outer peripheries thereof are slidably fitted in the pair of sliding holes 53, respectively. An output shaft 56 with an integrally formed pinion 57 engaging with the racks 55 is rotatably supported by ball bearings 58 arranged in the body 52, and the output shaft 56 is rotated by reciprocating of the rack member 54 on the basis of supplying and discharging of compressed air.
However, in accordance with this conventional oscillating actuator 51, since seal members 59 for sealing the compressed air are respectively attached to both end portions in the axial direction of the rack members 54 having the racks 55 formed in parts of the outer peripheries thereof, it is necessary to make an axial length of the rack member 54 longer than a length for a necessary number of teeth. Accordingly, there is a disadvantage that the whole of the actuator 51 is made in a large size. Since an air leakage is generated if the seal member 59 such as a packing or the like is interfered with a pinion chamber 60, it is necessary to secure a margin corresponding thereto in the axial length of the rack member 54.
Further, since each of the rack members 54 is formed in a solid columnar shape, and the columnar rack member 54 is manufactured by a high specific gravity material such as a steel or the like for the purpose of obtaining a desired strength, the weight of the rack member 54 is heavy, whereby there is a disadvantage that the weight of the whole of the actuator 51 is heavy. When the rack member 54 is heavy, it is necessary to make a working pressure for moving the rack member 54 large.
In the case of mounting this kind of oscillating actuator to a head portion of a robot or the like, it is particularly required to make the actuator in small size and light weight in view of a conveyable weight capacity of the robot and a tact time abbreviation. Accordingly, the rack and pinion type oscillating actuator which is heavier and larger than a vane type oscillating actuator tends to be avoided. On the other hand, it is pointed out that the vane type oscillating actuator has air leakage and unstableness in motion. Therefore, it is desired to make the rack and pinion type oscillating actuator small size and light weight.
Further, in this kind of oscillating actuator, there is a case that sliding abrasion powder (metal abrasion powder) generated when the rack member 54 slides within the sliding hole 53 deteriorates a lubricating fluid. In accordance with the conventional oscillating actuator 51, since the sliding surface of the seal member 59 overlaps with the sliding surface of the rack member 54, there is a case that the deteriorated lubricating fluid adversely influences a service life of the seal member 59.